Method and installation for the production of an aluminum sheet with a textured surface

ABSTRACT

A method for producing a sheet made of aluminum or an aluminum alloy, which is provided with a textured surface. According to the method, a cold rolled sheet is fed through the gap between two texturing rollers which are provided with a roughness pattern immediately after exiting a cold rolling mill, and the textured sheet is wound. The roughness pattern is transferred to the surface of the sheet by means of a force acting from the texturing rollers on the sheet. The installation for producing a cold rolled sheet made of aluminum or an aluminum alloy, which is provided with a textured surface, comprises a texturing rolling mill that encompasses texturing rollers and is disposed immediately after the cold rolling mill in the running direction (x) of the sheet. The method and installation make is possible to save a separate texturing pass and therefore one roller pass as opposed to methods known in prior art.

BACKGROUND OF THE INVENTION

The invention relates to a process and unit for producing a cold rolledstrip of aluminium or an aluminium alloy with a textured surfacecomprising passing a cold rolled strip immediately after cold rollingthrough a roll gap of two textured rolls bearing a roughness pattern,wherein the roughness pattern is transferred to the surface of the stripas a result of the force of the textured rolls acting on the strip, and,thereafter, coiling the textured strip.

In the automotive industry strips and sheets of aluminium alloys areemployed for the manufacture of bodywork parts, whereby the sheets areshape-formed by deep drawing or stretch drawing. Lubricants have to beemployed to carry out this deep drawing and other shape-forming steps.By pre-coating the strips or sheets in the rolling mill not only is theforming procedure simplified, but also optimal protection duringtransportation achieved.

In a procedure commonly used today the strip manufacturer coats the coldrolled strip with an oil or a water-soluble dry lubricant and theprepared strip supplied to the sheet-forming company for the purposes ofdeep drawing.

In the case of an aluminium strip that has been produced in the normalmanner using work rolls with a roll finish corresponding to amill-finish surface texture, the lubricants exhibit relatively pooradhesion and distribution.

The adhesion and distribution properties of dry lubricants on the stripsurface can be markedly improved by providing the surface of the stripwith a roughness pattern. To that end the roughening of the stripsurface is effected by transferring the roughness pattern on the workrolls to the surface of the strip during cold rolling of the strip.

Today, the roughness patterns provided on the surface of the aluminiumstrip to improve the adhesion and distribution of a dry lubricant thereare produced by work rolls which are roughened e.g. by electricaldischarge texturing (EDT), by electron beam texturing (EBT) or by thePRETEX method. All of these methods of roughen-ing result in a surfacetexture with irregularly distributed, closed “lubricant pockets”.

The above mentioned roughness patterns are produced on the surface ofthe strip in an additional cold rolling pass using a roll pass involvinga small thickness reduction approx. 0.05 to 15%. In practice thisadditional cold rolling pass incurs correspondingly greater productioncosts. In addition, in order to produce the roughness pattern, it isnecessary to change the work rolls that have a conven-tional roll-grindpattern for textured rolls.

A process and unit of the above mentioned kind is known from EP-A-O 945198.

The object of the present invention is to provide a process and a unitof the kind described at the start, by means of which the productioncosts for manufacturing textured strips can be reduced. A furtherobjective is to avoid the loss of capacity on a production unit causedby an additional texturing roll pass.

SUMMARY OF THE INVENTION

The object of the invention is achieved by providing a processcomprising passing a cold rolled strip immediately after cold rollingthrough a roll gap of two textured rolls bearing a roughness pattern,wherein the roughness pattern is transferred to the surface of the stripas a result of the force of the textured rolls acting on the strip, and,thereafter, coiling the textured strip.

With this process it is possible to dispense with a separate texturingroll pass and consequently save one roll pass compared with the state ofthe art method.

On performing the process according to the invention the cold rolledstrip is drawn through the roll gap and the texturing rolls turned bythe tension on the strip.

In order to adjust the thickness as uniformly as possible over the wholebreadth of the strip, the texturing rolls are preferably set at aconstant roll force.

To endow the strip surface with the above mentioned property whereby itacts as substrate for a dry lubricant, the texturing rolls are—toadvantage—roughened using electrical discharge texturing (EDT).

It has been found that the process according to the invention is alsosuitable for smoothing cold rolled strips. To that end it can also beproved advantageous to provide the texturing rolls with theconventional, simple roll grind that results in the so called “millfinish” surface quality. The rolls are only ground over their outersurface direction, i.e. the roll grind comprises a plurality of parallelgrooves distrib-uted over the outer surface of the rolls.

Preferred is an arrangement in which the texturing rolls in thetexturing roll stand are supported by intermediate rolls, which are inturn supported by backing rolls. The backing rolls may be arranged inseveral sets of rolls across the width of the intermediate rolls.

The backing rolls are preferably joined up in co-action to hydraulicpistons set at a constant force.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages, features and details of the invention are revealedin the following description of preferred exemplified embodiments andwith the aid of the drawing; this shows schematically in

FIG. 1: the end view of a unit for producing a strip with a texturedsurface;

FIG. 2: the front elevation of a texturing roll stand;

FIG. 3: the cross-section through the roll arrangement of a roll standshown in FIG. 2.

DETAILED DESCRIPTION

A unit for producing an aluminium strip with a textured surfaceaccording to FIG. 1 comprises a cold rolling mill 17 with two work rolls18, 20 forming a roll gap 19 and two backing rolls 22, 24 supporting thework rolls. The work rolls 18, 20 and the backing rolls 22, 24 aremounted in a mill stand 26 in a known manner.

Likewise installed in the stand 26 is a texturing roll stand 28 which issmaller than the cold rolling mill 17.

As shown in FIGS. 2 and 3, the texturing roll stand 28 exhibits twotexturing rolls 38,40 which delimit a roll gap 39 and are supported by apair of intermediate rolls 42, 44. Each pair of intermediate rolls 42,44 is supported by five sets of three backing rolls 46, 48. The backingrolls 46, 48 are mounted in beams 50, 52 which extend over the width ofthe rolls. The upper beam 50 is supported by an upper part 54 of theroll stand frame via hydraulic pressure type pistons 58, the lower beam52 lies directly on a lower part 56 of the roll stand frame. Both parts54, 56 of the roll stand frame may be moved towards and away from eachother by means of hydraulic raising or lowering pistons 60, 62 i.e. theroll gap 39 can be opened as desired viz., when no texturing pass isrequired, or when the necessary dimension for a texturing pass is beingadjusted. The roll force is adjusted via the hydraulic pistons 58 andthus the reduction in strip thickness during the texturing roll pass.The roll force is set by via the hydraulic compressive piston 58 andwith that the reduction in thickness of the strip during the texturingpass.

In order to produce the surface texture pattern, a cold rolled stripcoiled onto a reserve roll 14 is passed over a deflection roll 16 thenfed in the rolling direction x to the roll gap 19 of the cold rollingmill 17. After it emerges from the roll gap 19, the strip 12 enters theroll gap 39 of the texturing mill stand 28. On leaving the texturingmill stand 28 the strip 12 is deflected around two further deflectionrolls 30, 32 and coiled onto a spool 34. The thickness of the strip ischecked by a thick-ness measuring device 36 situated between thetexturing mill stand 28 and the second deflection roll 30. At the sametime, the second deflection roll 30 serves to check the flatness of thetextured strip 12.

The work rolls 18, 20 of the cold rolling mill 17 are driven and thestrip 12 is drawn into the roll gap 19 by the rolls themselves. Thetexturing rolls 38, 40 are not driven, the strip 12 must be drawnthrough the texturing roll stand. This is done by the driven spool 34.The braking action of the texturing rolls 38, 40 results in a stress-regulating effect, which leads to better flatness in the textured strip12.

The diameter of the texturing rolls 38, 40 is of course smaller than thediameter of the driven work rolls 18, 20 of the cold rolling mill 17.This produces a better texture in the strip surface with the result thata smaller reduction in thickness is necessary. The diameter of atexturing roll is e.g. around 350 mm.

1-12. (canceled) 13: A process for producing a strip of aluminium or analuminium alloy with a textured surface, comprising passing a coldrolled strip immediately after cold rolling through a roll gap of twotextured rolls bearing a roughness pattern, wherein the roughnesspattern is transferred to the surface of the strip as a result of theforce of the textured rolls acting on the strip, and, thereafter,coiling the textured strip. 14: A process according to claim 13,including drawing the cold rolled strip through the roll gap wherein thetexturing rolls are turned by tension applied to the strip. 15: Aprocess according to claim 13, including drawing the texturing rolls.16: A process according to claim 13, including sitting the texturingrolls at a constant roll force. 17: A process according to claim 13,including roughing the texturing rolls using the electrical dischargetexturing (EDT) method. 18: A process according to claim 13, wherein thetexturing rolls exhibit a roll grind comprising a plurality of parallelgrooves distributed over the outer face of the rolls. 19: A unit forproducing a cold rolled strip of aluminium or an aluminium alloy with atextured surface, comprising a cold rolling mill, and a texturing rollstand with texturing rolls immediately after the cold rolling mill,downstream in the direction of rolling (x). 20: A unit according toclaim 19, wherein the texturing rolls are connected to a drive facility.21: A Unit according to claim 19, wherein the texturing rolls in thetexturing roll stand are supported by intermediate rolls and theintermediate rolls are supported by backing rolls. 22: A unit accordingto claim 21, wherein a plurality of sets of backing rolls are arrangedover the width of the intermediate rolls. 23: A unit according to claim21, wherein the backing rolls are connected to hydraulic pistons set atconstant force. 24: A unit according to claim 19, wherein the texturingroll stand is mounted in the framework of the cold rolling mill.